Maybe a starter villain to help ease everyone into the concept, and then once that's over throw open the doors to the sandbox?

So would the starting village be something like Traverse Town or something? Since for some reason that seems to be the first thing to pop into my head. XD

How about Doctor Doom or Maleficent begin to take control of the multiverse with the Infinity Gauntlet?

<Snipped quote by Alan Hawke>

The Infinity Gems don't work outside their home universe, so probably not.

Well why not Earth? As in the earth where all these characters are supposed to be fictitious/non-existant? It could be our characters arrive through various means in around about the same area as The Incubators when they start harvesting peoples souls.
Although at that point I doubt our characters would be strong enough to fend them off for long so they'd have to retreat with the Incubators hot on their tail. Then we get to the whole bit of them being safe and asking questions about what happened, who each of them are, what to do. ect. :3

Also might be a good idea to drag in that exposition bit from the sign up onto here for future reference.

How about Doctor Doom or Maleficent begin to take control of the multiverse with the Infinity Gauntlet?

Also might be a good idea to drag in that exposition bit from the sign up onto here for future reference.

<Snipped quote by @Arty Fox>

Probably not a bad idea. Or maybe a link to that thread for anyone that sees this one first, since Psyga said he wasn't closing signups yet?

or another idea we start running for our lives on some sort of dangerous world where we're most likely going to die. I vote the Attack on Titan world, ho wants to become delicious?

ho wants to become delicious?